Silver(I)-mediated C-H amination of 2-alkenylanilines: Unique solvent-dependent migratory aptitude

Article abstract of DOI:10.1002/adsc.201400759

A highly effective silver(I)-mediated C-H amination of 2-alkenylanilines has been developed to afford a diverse range of substituted indoles. High functional group tolerance, broad substrate scope, simple/fast/high-yielding reaction, and recovery/reuse of the inexpensive silver oxidant are noteworthy. Furthermore, an uncommon migratory process of β-monosubstituted 2-alkenylanilines with solvent-dependence was demonstrated.

Full text of DOI:10.1002/adsc.201400759

UPDATES
DOI: 10.1002/adsc.201400759
ꢀ
Silver(I)-Mediated C H Amination of 2-Alkenylanilines: Unique
Solvent-Dependent Migratory Aptitude
So Won Youn,a,* Tae Yun Ko,a Min Jung Jang,a and Su San Janga
a
Center for New Directions in Organic Synthesis, Department of Chemistry and Research Institute for Natural Sciences,
Hanyang University, Seoul 133-791, Korea
Fax : (+82)-2-2299-0762; e-mail: sowony73@hanyang.ac.kr
Received: August 1, 2014; Revised: September 18, 2014; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201400759.
ꢀ
Abstract: A highly effective silver(I)-mediated C
Hegedus group.[2,3] Its rather limited substrate scope
has been significantly broadened by the beautiful
photocatalytic reaction of Zheng and co-workers.[4]
However, its practicality is yet to be solved due to the
requirement of a difficult-to-remove para-alkoxy-
phenyl group on the nitrogen atom, expensive transi-
tion metal catalysts, and a special experimental set-
up. Recently, our group reported a DDQ-mediated
H amination of 2-alkenylanilines has been devel-
oped to afford a diverse range of substituted in-
doles. High functional group tolerance, broad sub-
strate scope, simple/fast/high-yielding reaction, and
recovery/reuse of the inexpensive silver oxidant are
noteworthy. Furthermore, an uncommon migratory
process of b-monosubstituted 2-alkenylanilines with
solvent-dependence was demonstrated.
ꢀ
metal-free C H amination of 2-alkenylanilines for the
synthesis of a diverse array of substituted indoles in
excellent yields.[5] This facile and simple procedure
along with the use of easily removable Ts (para-tolu-
Keywords: cyclization; indoles; migration; oxida-
tion; silver
AHCTUNGTREGeNNNU nesulfonyl) as an N-protecting group has significant-
ly improved the efficiency and practicality of indole
ꢀ
formation via C H amination of 2-alkenylanilines.
However, there was still a limitation which is the in-
ꢀ
Intramolecular oxidative C H amination is one of the compatibility of alkyl-substituted alkene derivatives
straightforward and powerful routes to highly valua- (R ¼ alkyl in Scheme 1) and a methyl substituent (in
ble, bioactive nitrogen heterocycles.[1] Among them, some cases when R=4-MeC6H4 or R’’=Me) under
Pd(II)-catalyzed C H amination of 2-alkenylanilines strong oxidation conditions (i.e., DDQ). Therefore,
has been considered as an effective pathway toward we were interested in developing a more general and
the indole skeleton, since the pioneering work of the
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Scheme 1. Ag(I)-mediated oxidative C H amination of 2-alkenylanilines.
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So Won Youn et al.
Table 1. Optimization studies.[a]
efficient procedure with high functional group toler-
ance and wide substrate scope.
Herein we disclose a highly effective Ag(I)-mediat-
ꢀ
ed C H amination of 2-alkenylanilines to construct
a wide range of substituted indoles (Scheme 1).[6] In
particular, this newly developed method offers signifi-
cantly improved substrate scope and functional group
tolerance through the use of Ag2CO3 as a relatively
inexpensive Ag oxidant which can be easily recovered
and reused. The operationally straightforward and
simple procedure, notably short reaction time, and un-
precedented, unique migratory process with solvent-
dependence are also highly noteworthy.
Entry
Ag(I) (equiv.)
Solvent
Yield [%][b]
1
2
3
4
5
6
7
8
Ag2CO3 (1)
Ag2O (1)
AgOAc (1)
Ag(O2CCF3) (1)
AgOTs (1)
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
ClCH2CH2Cl
toluene
heptane
1,4-dioxane
MeCN
DMF
DMSO
t-BuOH
DMF
DMF
DMF
DMF
heptane
ClCH2CH2Cl
heptane
heptane
54 (1:0.2)[c]
26
45
19
Considering the recent advances of various Ag-
mediated oxidative processes in heterocyclic synthe-
sis,[7,8] we envisioned the potential application of such
an oxidation system for the desired indole formation.
We began our investigations on a variety of Ag salts
as an oxidant using 1a as the test substrate (Table 1).
Gratifyingly, it was found that Ag2CO3 promoted this
–
31
Ag2CO3 (1)
Ag2CO3 (1)
Ag2CO3 (1)
Ag2CO3 (1)
Ag2CO3 (1)
Ag2CO3 (1)
Ag2CO3 (1)
Ag2CO3 (0.5)
Ag2CO3 (1.3)
Ag2CO3 (2)
Ag2CO3 (1.3)
Ag2CO3 (1.3)
Ag2CO3 (1.3)
Ag2CO3 (1.3)
Ag2CO3 (1.3)
51 (1:0.2)[c]
(77)
9
52
(78)
79
39
(47)
(82)
(77)
(83)
10[d]
11
12
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C H amination reaction to afford 2a along with 2a’
13[e]
14[f]
15[g]
16[h]
17[i]
18[j]
19[i,k]
20[i,l]
resulting from a phenyl migration in 54% yield
(entry 1). Among a variety of Ag salts examined,
Ag2CO3 was the most effective oxidant for this trans-
formation (entries 1–5). Various solvents were exam-
ined, and DMF appeared preferable with regard to re-
action time and product yield (entries 6–12). Further
optimization of reaction conditions (entries 13–16) se-
cured a high yield of indole 2a after a very short reac-
tion time (83%, 1.3 equiv. Ag2CO3 in 0.025M DMF at
1508C for 30 min, entry 16). On the other hand,
during the solvent screening study, 1,2-phenyl migra-
tion was observed in both dichloroethane (DCE) and
heptane, giving the mixture of 2- and 3-phenyl-substi-
tuted indole products (2a:2a’=1:0.2, entries 1 and 7).
This unexpected finding is of great interest since the
1,2-carbon shift has been generally observed in the re-
lated reaction of only b,b-disubstituted 2-alkenylani-
line derivatives[4,5,9] with the exception of a single ex-
ample of a b-monosubstituted 2-alkenylaniline bear-
ing an electron-rich substituent (e.g., 1f with 4-
MeOC6H4) in our previous work.[5] Prompted by this
initial result, we subsequently turned our efforts to
find more effective reaction conditions for the 1,2-
aryl migration. It was found that the use of both hep-
tane as a solvent at higher reaction temperature
(1508C) and Ns (para-nitrobenzenesulfonyl) group in-
stead of Ts as the N-protecting group was beneficial
for both higher chemical yield (2a+2a’) and ratio of
6aB to 6aA, respectively.[10] Finally, optimal reaction
(89) (1:0.2)[c]
(42) (1:0.2)[c]
77 (1:0.2)[c]
(88) (1:0.8)[c]
[a]
All reactions were carried out 3–5 times repetitively and
the average values of both yields and ratios are given.
Except for entries 19 and 20, all reactions used 1a as
a substrate.
Yields were determined by H NMR using trichloroethy-
lene as an internal standard. Value in parentheses indi-
[b]
[c]
1
cates an isolated yield.
Ratios of inseparable isomers (2a:2a’ or 6aA:6aB) were
determined by 1H NMR.
[d]
[e]
[f]
[g]
[h]
[i]
For 2.5 h.
For 48 h.
For 3 h.
For 1 h.
In DMF (0.025M) at 1508C for 0.5 h.
At 1508C for 12 h.
At 1508C for 5 h.
Using N-Bs-substituted substrate instead of 1a.
Using N-Ns-substituted substrate (5a) instead of 1a. Ts=
para-toluenesulfonyl, Bs=benzenesulfonyl, Ns=para-ni-
trobenzenesulfonyl.
[j]
[k]
[l]
With the optimized reaction conditions in hand, we
conditions were established as entry 20 in Table 1, first set out to explore the substrate scope of the pro-
giving 6a in good combined yields (88%, 6aA:6aB= cess in DMF (Table 2). Both terminal (mono- and 1,1-
1:0.8), albeit with a longer reaction time than that in disubstituted, entries 15 and 18–20) and internal (1,2-
DMF. To the best of our knowledge, this represents disubstituted) alkenes were well tolerated for this re-
the first example of 1,2-phenyl migration in the relat- action. Aryl-substituted alkenes (R3 =aryl) underwent
ꢀ
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ed C H amination of 2-styrylaniline derivatives bear- C H amination smoothly to afford the corresponding
ing one substituent at the b position of alkenes. indoles in good yields irrespective of the aryl substitu-
2
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Silver(I)-Mediated C H Amination of 2-Alkenylanilines
Table 2. Substrate scope: mono- or disubstituted alkene de-
rivatives.
tivity (entries 21–28). It is noteworthy that this pro-
cess can tolerate various functional groups such as
methoxy, halogen, nitro, heteroaryl groups as well as
the methyl group which is prone to oxidation.[11]
Subsequently, we investigated the reaction of tri-
substituted alkenyl derivatives under the standard re-
action conditions (Table 3). All reactions proceeded
successfully to afford the corresponding 2,3-disubsti-
tuted indoles. When the b,b-disubstituted 2-alkenyla-
nilines have an alkyl and an aryl substituent at the
b position, a selective migration of the aryl group was
observed in good yields (entries 1 and 2). In the case
of b,b-dialkyl-substituted substrate 3d, the ring expan-
sion product 4d was obtained through an alkyl group
migration (entry 4). Meanwhile, b,b-diaryl-substituted
substrates showed the higher migratory aptitude of an
electron-rich aryl group than an electron-deficient
one (entries 5–8). These findings might provide im-
portant insights into the reaction mechanism, suggest-
ing that benzylic carbocations and cationic rearrange-
ments are presumably involved.[4,5,9]
Entry R1
R2
R3
Time Yield
[h]
[%][a]
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Ph (1a)
0.5
0.5
0.5
0.5
83 (72)[b] (2a)
72 (2b)
74 (2c)
4-MeC6H4 (1b)
3-MeC6H4 (1c)
2-MeC6H4 (1d)
72 (2d)
2,4,6-Me3C6H2 (1e) 0.5
96 (2e)
0.75 73 (2f)
4-MeOC6H4 (1f)
3-MeOC6H4 (1g)
4-ClC6H4 (1h)
4-NO2C6H4 (1i)
3-CF3C6H4 (1j)
1-naphthyl (1k)
3-thienyl (1l)
3-furanyl (1m)
2-pyridyl (1n)
H (1o)
n-Hex (1p)
c-Hex (1q)
R=Ph (1r)
R=Me (1s)
0.5
1
0.5
1
0.5
4
0.5
0.5
0.5
0.5
0.5
2
77 (2g)
60 (2h)
79 (2i)
68 (2j)
76 (2k)
75 (2l)
61 (2m)
73 (2n)
79 (2o)
74 (2p)
80 (2q)
92 (2r)
90 (2s)
96 (2t)
9
10
11
12
13
14
15
16
17
18
19
20
Next, we turned our attention to the 1,2-carbon
shift reaction of b-monosubstituted N-Ns-2-alkenyl-
AHCTUNGTREGUNaNN niline 5 under the optimized reaction conditions
(Table 4). Compared to the reactions in DMF, this
protocol generally required longer reaction times. In
some cases, DCE was needed as a co-solvent due to
the low solubility of the substrates in only heptane
which could result in very low conversion. As shown
in Table 4, a variety of (hetero)aryl groups could mi-
grate to give the corresponding rearranged 3-substi-
tuted indole 6B along with unrearranged 6A (en-
tries 1–11 and 13, 14), whereas 1,2-alkyl migration
failed to take place (entry 12). While only little steric
effect of the migrating group with ortho substituents
(entries 5–7 and 10) was apparent, its electronic densi-
ty seems to play an important role to determine the
degree of 1,2-aryl migration: electron-rich aryl groups
migrate more favorably (entries 1 and 9, 10 vs. en-
tries 2–8), providing further evidence for cationic re-
arrangements via a phenonium ion intermediate.[4,5,9]
1.5
0.3
R=c-Pr (1t)
21
22
23
24
25
26
27
28
OMe H
Me
Cl
NO2
H
H
Ph (1u)
Ph (1v)
Ph (1w)
Ph (1x)
0.17 55 (2u)
86 (2v)
0.08 71(2w)
H
H
H
1
0.5
0.5
1
1
2
48 (2x)
66 (2y)
84 (2z)
88 (2aa)
75 (2ab)
OMe Ph (1y)
Me Ph (1z)
Cl
H
H
Ph (1aa)
NO2 Ph (1ab)
[a]
[b]
Isolated yield.
1.1 g of 1a was used.
ꢀ
tion, showing little electronic and steric dependence
To investigate the synthetic potential of the C H
(entries 1–11). Heteroaromatic motifs such as thio- amination method presented herein, the reaction of
phene, furan, and pyridine could be also incorporated 1a was carried out on a gram scale (Table 2, entry 1).
as a substituent at the alkene terminus (entries 12– To our delight, the desired product 2a was obtained in
14). Noteworthy is the fact that alkyl-substituted al- 72% yield. Furthermore, recovery and recycling of
kenes (R3 =alkyl) were also well tolerated in this re- Ag2CO3 could alleviate the cost and waste problem to
action, leading to the desired indole products in good use stoichiometric amounts of Ag2CO3 in this reac-
yields (entries 16, 17 and 19, 20). On the other hand, tion, albeit the relative low cost of Ag2CO3 among
electron-withdrawing substituents at the alkene silver sources is favorable. The regenerated Ag2CO3
moiety (e.g., R3 =ketones, esters, amides, nitrile) re- could effectively promote this oxidative C H amina-
ꢀ
sulted in no reaction with mostly recovered starting tion of 1a without the loss of activity, with four con-
materials (not shown), alluding to the involvement of secutive runs providing comparable yields [Eq.
an electrophilic addition to a tethered alkene. Both (1)].[12]
electron-donating and electron-withdrawing substitu-
To gain further mechanistic insight into this reac-
ents residing on the aromatic moiety of N-Ts-2-styry- tion, a series of control experiments were performed.
lanilines (R1, R2) had no significant effect on the reac- When substrate 1a was subjected to the optimal reac-
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Table 3. Oxidative cyclization reactions of trisubstituted alkene derivatives.[a]
Entry
Substrate
Time [h]
Product
Yield [%][b]
82
1
3a
0.5
4a
2
3b
0.5
4b
92
3
4
3c
0.5
0.5
4c
93
63
3d
4d
5
6
7
8
3e
3f
3g
3h
Ar1 =4-MeOC6H4, Ar2 =Ph
Ar1 =4-MeC6H4, Ar2 =Ph
Ar1 =Ar2 =Ph
0.5
1
5
4e
4f
4g
4h
(6:1)
(2.5:1)
–
89
86
77
83
Ar1 =4-ClC6H4, Ar2 =Ph
0.5
(1:1.2)
[a]
Same reaction conditions as Table 2.
Isolated yield.
Determined by H NMR.
[b]
[c]
1
tion conditions in the presence of TEMPO (2,2,6,6-
tetramethylpiperidine-N-oxyl), the reaction proceed-
ed as usual to give 2a in 86% yield [Eq. (2)]. On the
contrary, BHT (3,5-di-tert-butyl-4-hydroxytoluene)
did exert a deleterious effect on the reaction.[13] We
speculated that a radical might be involved but its ox-
idation to the corresponding benzylic carbocation
(B!C, Scheme 2) could be too fast for TEMPO to
inhibit the reaction. Alternatively, it has been also re-
ported that the reaction rate of resonance stabilized
benzylic radicals with TEMPO is much slower than
that of alkyl radicals and its reaction is reversible
even at ambient temperature.[14] While the detrimen-
tal effect of BHT could infer that a radical might be
involved in this reaction, it cannot be completely ex-
cluded that this outcome could be attributed to its
direct reaction with Ag2CO3, leading to depletion of
Ag oxidant and ineffective reaction thus shutting
down the indole formation reactions to a large extent.
Radical clock experiments[15] using 1t and 1z were
conducted under the optimized conditions [Eq. (3)].
The first gave indole 2t in very high yield (96%) as
the sole product with the cyclopropyl ring remaining
intact, while the latter led to a complex mixture in-
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Silver(I)-Mediated C H Amination of 2-Alkenylanilines
Table 4. Substrate scope of 1,2-migration reaction.
Entry
5
R1
R2
R3
Time [h]
6
Yield [%][a] (6A:6B)[b]
1
2
3
4
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
Ph
12
12
12
24
24
7
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
88 (1:0.8)
86 (1:1.5)
95 (1:2.1)
75 (1:1.9)
78 (1:2.4)
86 (1:3.1)
91 (1:3.9)
80 (1:4.5)
84 (1:0.95)
65 (1:0.5)
87 (1:2.5)
70 (1:0)
4-MeC6H4
4-MeOC6H4
3,4-(MeO)2C6H3
2,6-(MeO)2C6H3
2,4-(MeO)2C6H3
2,4,6-(MeO)3C6H2
3,4-(-OCH2O-)C6H3
4-ClC6H4
1-naphthyl
3-thienyl
c-Hex
Ph
Ph
5
6[c]
7[c]
8[c]
9[c]
10
11[c]
12
13
14[c]
7
4
7.5
24
24
24
24
24
85 (1:1.4)
78 (1:0.8)
[a]
Isolated yield of inseparable isomers (6A+6B).
Ratios of inseparable isomers were determined by H NMR.
In heptane/ClCH2CH2Cl (4:1, 0.05M). Substrate was dissolved in ClCH2CH2Cl first and then heptane was added in the
mixture.
[b]
[c]
1
Scheme 2. Proposed mechanism.
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cluding a couple of unidentified compounds. Different nation of 2-alkenylanilines using an inexpensive and
reaction outcomes of 1t and 1z may be understood on reusable Ag oxidant, demonstrating that the method
ꢀ
the basis of literature precedents reporting that the presented herein arguably surpasses other related C
presence of a phenyl substituent exerts a strong influ- H amination processes. Noteworthy is that a unique
ence on the ring opening reaction rates of cycloprop- 1,2-(hetero)aryl group migration of b-monosubstitut-
yl-containing radicals (cyclopropylmethyl: 1.2ꢁ108 sꢀ1, ed 2-alkenylanilines was observed to give the corre-
cyclopropylbenzyl: 2.7ꢁ105 sꢀ1, (2-phenylcyclopro- sponding rearranged 3-substituted indoles along with
pyl)benzyl: 3.6ꢁ108 sꢀ1): the cyclopropylbenzyl radical the unrearranged 2-substituted ones, depending on
undergoes a reversible ring opening reaction with the the reaction medium. Our experimental findings sug-
ring-closed form being thermodynamically preferred, gest that this oxidative cyclization reaction implicates
while resonance stabilization of the ring-opened radi- a radical cation generated by SET and a phenonium
cal by another phenyl group on the cylcopropyl ring ion intermediate for a subsequent migratorial process.
skeleton [e.g., (2-phenylcyclopropyl)benzyl radical] Further investigations to construct other privileged
facilitates the ring opening reaction.[15] We surmised heterocyclic scaffolds with detailed mechanistic stud-
that a ring opening reaction of the cyclopropylbenzyl ies are currently underway in our laboratory.
radical derived from 1t might be slower than its com-
petitive oxidation to benzylic cation (B!C, Sche-
me 2),[4,15c–e] whereas the reaction using 1z, in which Experimental Section
a phenyl group would allow for a faster ring cleavage
to result in a benzyl radical,[15b,e] led to a complicated General Procedure
mixture.
Substrate 1, 3 or 5 (0.065 mmol, 1 equiv.) and Ag2CO3
(23.4 mg, 0.084 mmol, 1.3 equiv.) were dissolved in DMF
Although clearly detailed mechanistic studies are
needed to clarify the mechanism in these reactions,
(2.6 mL, 0.025M) or heptane (1.3 mL, 0.05M) under an
a plausible mechanistic proposal is presented in
Scheme 2.[7,8] Nitrogen radical cation A generated
from the substrate (1, 3, or 5) with Ag(I) salt under-
goes an electrophilic addition to the tethered alkene
to afford a benzylic radical B with the loss of
a proton. Subsequently, single-electron transfer (SET)
from B to Ag(I) to produce the benzylic carbocation
C followed by the deprotonation forms the desired
indole product 2 via path a (when R3 =H). Note that
a silver mirror is observed during reaction.
In the case of b,b-disubstituted 2-alkenylanilines
(R2 or R3 =aryl), a migratorial process can occur via
a phenonium ion intermediate D or D’ through path
b or c to give carbocation intermediate E or E’, re-
spectively. Finally, loss of a proton produces the de-
sired product 4A/4B.[16] While the reason for different
reaction pathways of 5 (R2 =aryl, R3 =H) in heptane
or DCE solvent remains unclear and difficult to ex-
plain at this stage, rearranged indole 6B can be
formed similarly through C!D!E along with un-
rearranged indole 6A, which might form directly from
C or bypassing through C!D!C. An alternative
mechanistic pathway involving a nitrogen-centered
radical in the initial step could also be invoked.
argon atmosphere. The resulting mixture was stirred at
1508C for the reported time under an argon atmosphere.
After the reaction was completed, the reaction mixture was
concentrated under vacuum. The residue was purified by
column chromatography on silica gel to give the correspond-
ing product.
Acknowledgements
This work was supported by both Basic Science Research
Program and Nano·Material Technology Department Pro-
gram through the National Research Foundation of Korea
(NRF) funded by the Ministry of Education and MSIP (Nos.
2012R1A1A2041471, 2012M3A7B4049654, and 2014-
011165).
References
ꢀ
[1] For selected reviews on transition metal-catalyzed C H
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1998, 98, 675; b) A. Minatti, K. MuÇiz, Chem. Soc. Rev.
2007, 36, 1142; c) F. Cardona, A. Goti, Nat. Chem.
2009, 1, 269; d) P. Thansandote, M. Lautens, Chem.
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Stahl, Chem. Rev. 2011, 111, 2981; f) J. L. Jeffrey, R.
Sarpong, Chem. Sci. 2013, 4, 4092; g) J. Bariwalab, E.
Van der Eycken, Chem. Soc. Rev. 2013, 42, 9283; h) M.-
L. Louillat, F. W. Patureau, Chem. Soc. Rev. 2014, 43,
901.
In summary, we have developed a highly effective
ꢀ
Ag(I)-mediated C H amination of 2-alkenylanilines
to construct a diverse range of substituted indoles,
one of the most significant heterocycles found in nu-
merous natural products, pharmaceuticals, and other
functional molecules.[6] This enabling protocol offers
a notably simple and straightforward approach with
high functional group tolerance, broad substrate
scope, high efficiency and practicality, and short reac-
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ꢀ
tion time (in DMF) for indole synthesis via C H ami-
6
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UPDATES
So Won Youn et al.
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report, it was demonstrated that steric effects favor
a ring opening reaction at the less substituted carbon
atom (via path e). In our protocol, however, an alkene
substituent at the b position (i.e., R2, R3 of C in
Scheme 2) is more likely to take part in the formation
of a phenonium ion intermediate (D or D’) based on
the aforementioned outcomes (i.e., only 6lA formation
from 5l and migration degree depending on the elec-
tron density of substituent R3 in substrate 5). Another
conceivable mechanism involves the initial activation
of alkene by coordination to Ag(I) (G) which is fol-
lowed by nucleophilic attack by either sulfonamide
(path f) or ipso carbon of arene.
2011, 67, 4449, and refs.[8a,b,d]
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8
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Adv. Synth. Catal. 0000, 000, 0 – 0
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These are not the final page numbers!

UPDATES
ꢀ
Silver(I)-Mediated C H Amination of 2-Alkenylanilines:
Unique Solvent-Dependent Migratory Aptitude
9
Adv. Synth. Catal. 2014, 356, 1 – 9
So Won Youn,* Tae Yun Ko, Min Jung Jang, Su San Jang
Adv. Synth. Catal. 0000, 000, 0 – 0
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
9
ÞÞ
These are not the final page numbers!